U.S. patent number 4,113,417 [Application Number 05/760,140] was granted by the patent office on 1978-09-12 for combustion of hot gases of low calorific power.
This patent grant is currently assigned to Stein Industrie. Invention is credited to Jean Deruelle.
United States Patent |
4,113,417 |
Deruelle |
September 12, 1978 |
**Please see images for:
( Certificate of Correction ) ** |
Combustion of hot gases of low calorific power
Abstract
The complete combustion of hot gases of low calorific power is
effected by introducing the gases into a combustion chamber at a
pressure close to atmospheric pressure and at a temperature of
between 600.degree. and 900.degree. C, by introducing at burner
level primary air to a maximum of 80% of the stoichiometric
proportion, by supplying secondary air near the base of the flame
in an excess relation to the stoichiometric amount so that the
flame temperature is between 1,000.degree. and 1,300.degree. C and
by discharging the combustion products from the combustion chamber
by means of a chimney.
Inventors: |
Deruelle; Jean (St. Avold,
FR) |
Assignee: |
Stein Industrie
(Velizy-Villacoublay (Yvelines), FR)
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Family
ID: |
26218590 |
Appl.
No.: |
05/760,140 |
Filed: |
January 6, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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628768 |
Nov 4, 1975 |
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Foreign Application Priority Data
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Nov 6, 1974 [FR] |
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74 36828 |
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Current U.S.
Class: |
431/5; 431/10;
431/12 |
Current CPC
Class: |
F23G
5/46 (20130101); F23G 7/06 (20130101); F23D
2900/14002 (20130101) |
Current International
Class: |
F23G
7/06 (20060101); F23G 5/46 (20060101); F23D
013/20 () |
Field of
Search: |
;431/5,10,2,202,12
;110/8A ;23/277R,277C |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Favors; Edward G.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Parent Case Text
This is a division of application Ser. No. 628,768 filed Nov. 4,
1975 (now pending).
Claims
I claim:
1. A process for the complete combustion of hot gases of low
calorific power, such as reducing smoke of rich gases and
by-products of the carbonisation of coal, which gases are available
at a pressure close to atmospheric pressure, said process using at
least one burner in a combustion chamber having means for
introducing primary air and means for introducing secondary air and
comprising the steps of:
(a) introducing the gases into the combustion chamber at the
available pressure close to atmospheric pressure and at a
temperature of between 600.degree. and 900.degree. C,
(b) introducing primary air at burner level in an amount limited to
a maximum of 80% of the stoichiometric proportion,
(c) supplying secondary air near the base of the flame in an excess
relation to the stoichiometric amount such that the flame
temperature is between 1,000.degree. and 1,300.degree. C, and
(d) discharging the combustion products from the combustion chamber
by means of a chimney.
2. The process according to claim 1, in which the gases are
introduced into the combustion chamber at a temperature of about
750.degree. C.
3. The process according to claim 1, in which the chimney is a
natural draught chimney and the flame temperature is adjusted to
about 1,100.degree. C.
4. The process according to claim 1, in which the chimney is a
forced draught chimney working with an exhauster drawing all the
hot smoke through a heat exchanger, and the flame is adjusted to a
temperature of about 1,200.degree. C.
5. The process according to claim 1, including the step of
introducing a part of the secondary air through apertures so
disposed as to cool the walls of the combustion chamber by bathing
the walls.
6. The process according to claim 1, including the step of diluting
the combustion products with cold air to obtain an outlet
temperature below 600.degree. C.
7. The process according to claim 1, in which during at least a
part of the operating periods at least a part of the hot smoke is
branched off through a heat exchanger.
8. A process for the complete combustion of hot gases of low
calorific power, such as reducing smoke of rich gases and
by-products of the carbonisation of coal, which gases are available
at a pressure close to atmospheric pressure, said process using at
least one burner in a combustion chamber having means for
introducing primary air and means for introducing secondary air and
comprising the steps of:
(a) introducing the gases into the combustion chamber at the
available pressure close to atmospheric pressure and at a
temperature of between 600.degree. and 900.degree. C,
(b) introducing primary air at burner level in an amount limited to
a maximum of 80% of the stoichiometric proportion,
(c) supplying secondary air near the base of the flame by forming
an arch surrounding the flame and in an excess relation to the
stoichiometric amount such that the flame temperature is between
1,000.degree. and 1,300.degree. C, and
(d) discharging the combustion products from the combustion chamber
by means of a chimney.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for the complete combustion of
hot gases of low calorific power, such as reducing smoke of rich
gases and by-products of the carbonisation of coal, which gases are
available under a pressure close to atmospheric pressure, which
process uses at least one burner in a combustion chamber having
means for introducing primary air and means for introducing
secondary air. The invention also relates to a combustion chamber
for carrying out the process.
2. Description of the Prior Art
The by-products of a coal pyrolysis installation, such as a rotary
furnace, or a rotary hearth furnace, or a direct-fired furnace, are
in a gaseous state and entrain fine solid products, such as carbon
black, soot or coal dust, and condensible products such as tars or
benzenes.
In conventional pyrolysis processes these by-products are generally
subjected to sufficient cooling to achieve complete condensation,
thereby making it possible to obtain in the carbonisation plant the
negative pressure necessary for applying suction to the by-product
with the aid of known means, such as extractor fans. If on the
other hand it is desired to burn these by-products immediately at
the outlet of the pyrolysis furnace, difficulties are encountered
in transferring the gases from the pyrolysis furnace to the
combustion furnace, in achieving complete combustion of the
suspended particles, and finally in achieving the negative pressure
necessary for the extraction of the gases because of the high
temperature.
There are innumerable disappointing inventions relating to the
collection of charging gases in coke oven plants. In particular,
techniques aiming to burn the impurities lead to only very partial
results, combustion being incomplete. Furthermore, equipment is
periodically destroyed by explosions or local overheating.
A combustion chamber for the combustion of lean gases is known from
U.S. Pat. No. 2,920,689. Air for combustion is supplied by a fan
and divided into primary air and secondary air which are
respectively supplied through valves to nozzles from which they
pass out at high speed and with turbulence.
Furthermore, from French Pat. No. 2,193,178 a process is known for
the extinction of stoichiometric combustion products by the
injection of air with a view to limiting to 525.degree. C. the
temperature of the gases discharged to the atmosphere. Moreover, an
arrangement comprising two combustion chambers followed by an
extinction chamber is known from French Pat. No. 2,065,890.
These arrangements have the major disadvantage of entailing the
formation of a high-intensity turbulent flame, thereby making it
necessary to use expensive refractory materials and to take special
precautions against the risk of extinction and explosion, for
example by maintaining a pilot flame. Moreover, stoichiometric
proportions are difficult to maintain for gases whose calorific
power may vary, as is frequently the case with numerous lean gases
occuring as by-products of industrial processes, particularly when
they contain crackable constituents at high temperature of high
calorific power, such as carbon black and higher hydrocarbons.
SUMMARY
The aim of the invention is to propose a process and a combustion
chamber making it possible to achieve complete combustion and
perfect smoke removal without risk of explosion or damage to the
plant, while producing a negative pressure favourable to the
collection and evacuation of the gases.
In the process of the invention this aim is achieved through the
fact that the gases are introduced into the combustion chamber at
the available pressure close to atmospheric pressure and at a
temperature between 600.degree. and 900.degree. C., the primary air
is introduced at burner level in an amount limited to a maximum of
80% of the stoichiometric proportion, the secondary air is supplied
near the base of the flame and in an excess in relation to the
stoichiometric amount such that the flame temperature is between
1,000.degree. and 1,300.degree. C., and the combustion products are
discharged outside the combustion chamber by means of a
chimney.
In this manner it is ensured that the carbon black and the high
hydrocarbons will be completely burned thanks to perfect combustion
ensuring good consumption of smoke. This result is interesting when
it is known that it is difficult to achieve complete combustion of
crackable products having high calorific power when they are mixed
with considerable gaseous ballast. Combustion is achieved
practically without turbulence.
It is advantageous to introduce the gases into the combustion
chamber at a temperature of about 750.degree. C. and to adjust the
flame temperature to about 1,100.degree. C.
An advantageous expedient is to introduce a part of the secondary
air through apertures arranged to effect cooling by bathing the
walls of the combustion chamber.
In this way it is possible to obtain high combustion temperatures
without having to make the combustion chamber of expensive
refractory material. The combination of the bathing of the walls by
fresh air and the absence of turbulence is in fact very favourable
for maintaining a low wall temperature.
The combustion chamber according to the invention comprises in
combination: a vertical wall connected at the top to a chimney; a
base plate in which is disposed at least one burner comprising a
nozzle supplying gas at a pressure close to atmospheric and means
of supplying forced primary air for combustion, the said base plate
in addition being provided with peripheral nozzles directed towards
a point situated above the burner and having means of supplying
forced secondary air for combustion; control means controlling the
flow of air for combustion in dependence on the temperature of the
upper portion of the chamber, and control means controlling the
distribution of primary and secondary air flows in dependence on
the temperature of the flame.
In this way, the secondary air forms a kind of arch surrounding the
flame and effects perfect smoke-consuming combustion.
It is advantageous for the base plate to be provided in addition
with vertical peripheral apertures admitting air for bathing the
vertical walls, and for the base plate to have a projection
surrounding the peripheral nozzles of the burners.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical axial section of a combustion chamber
according to the invention and which contains a single burner,
FIG. 2 is a plan view of the base plate of an alternative
combustion chamber according to the invention and which contains
three burners.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, there is illustrated a combustion chamber
which has vertical walls and which is given the general reference
1, this chamber being connected at the top to a natural draught
chimney 3. A burner 12 and air inlet 14 are disposed in the base
plate 11 of the chamber 1, as will be explained below.
A pipe (not shown) supplies hot gases having low calorific power to
the nozzle 13 of the burner 12 which includes the air inlet duct 14
supplying primary air for combustion delivered by a fan 21, the
flow of which is measured by a diaphragm 15 and is regulated by a
damper 16 controlled by first regulating means shown as a
thermocouple 17 measuring the temperature at the top of the chamber
1, which is connected to the chimney 3.
The secondary air is introduced into the chamber through oblique
convergent nozzles 18 directed towards the flame appearing at the
tip of the burner 12. The Applicants' experience has shown that an
angle .alpha. close to 40.degree. is advantageous. The nozzles 18
are supplied with air by means of a wind box 19, which in turn is
fed with air by a fan (not shown) or by a branch of the primary air
supply pipe, this branch being adjustable by means of a damper.
In either case the flow of secondary air is controlled by second
regulating means shown as a thermocouple 20.
The control means effect regulation in such a manner that the
conditions previously indicated for the definition of the main
characteristic of the invention are achieved, that is to say for
introduction of the gases at a temperature between 600.degree. and
800.degree. C., primary air limited to 80% of the stoichiometric
proportion, an excess of secondary air such that the flame
temperature is between 1,000.degree. and 1,300.degree. C. Preferred
adjustments will be 750.degree. C. for the admission temperature
and 1,100.degree. C. for the flame temperature. A peripheral
projection 10 surrounds the nozzles 18 and improves the directivity
of the secondary air.
A further quantity of secondary air may be introduced into the
combustion chamber 1 through apertures 22 distributed around the
periphery of the base plate 11. These apertures 22 are disposed
vertically, so that the air which passes through them passes into
the combustion chamber 1 so as to bathe the vertical walls of the
chamber 1 and thus cool them. It is advantageous for the apertures
22 to be adjustable. It is preferable for the air to enter the
apertures 22 under the action of the negative pressure prevailing
in the chamber. Alternatively, the air can be supplied to the
apertures 22 by means of a fan or of a branch from the wind box
19.
A fan 23 makes it possible to blow cold air through a pipe 25 at
the base of the chimney 3 so that, by adjusting a damper 26
controlled by a thermocouple 24, an outlet temperature of the
chamber lower than 600.degree. C. can be obtained.
A heat exchanger 4 makes it possible to use the sensible heat of
the smoke during at least part of the operating periods. To this
end it is possible to produce a forced circulation through the heat
exchanger 4 by means of a branch pipe 41, with the aid of an
exhaust fan 43 provided with a damper 44 controlled by the
thermocouple 24 and finally through an independent chimney 42.
The installation may be completed by any usual subsidiary devices,
for example starting burners (not shown) to enable the combustion
chamber to reach its operating temperature, flame detection cells,
and any other usual safety device.
The process may be applied to gases such as those defined in the
preamble, without this constituting a limitation; it may for
example advantageously be applied to the gases coming from a coal
pyrolysis plant carrying out the process described in French Patent
Application No. 74 22402 of June 27, 1974, having the title
"Process for the production of pulverulent coke and reactive coke
in grains".
Experiments carried out by the Applicants surprisingly show that,
when applied to pyrolysis gases at 750.degree. C. which are
obtained from the process mentioned above, the process of the
invention makes it possible to obtain at the outlet of the chimney
3 an exhaust to the atmosphere which is practically invisible and
is even invisible in a wreath of water vapour.
In this case the gases had a net calorific value, including
sensible heat, of 2600 kcal/kg at 750.degree. C. The termal load of
the chamber attained 25000 th/h, and produced in the gas supply
pipe a negative pressure of about 2 millibars for a negative
pressure of the combustion chamber of 3 millibars. The combustion
conditions were very stable with a primary air flow of 18,000 cubic
meters per hour, a central secondary air flow of 22,000 cubic
meters per hour, and a peripheral secondary air flow of 20,000
cubic meters per hour.
FIG. 2 shows a variant of the apparatus illustrated in FIG. 1,
comprising three burners 12. The same reference numerals designate
the same parts as in FIG. 1.
It will be observed that the process utilise an internal regulation
arrangement which it would appear helpful to recapitulate:
The air for combustion is regulated by the first regulating means
17 in dependence on the temperature measured in the top part of the
combustion chamber;
The distribution between primary air and secondary air in the
burner is regulated by the second regulating means 20 in dependence
on the temperature of the flame. In practice it will be easy to
regulate it in dependence on the temperature radiated at burner
level onto the walls, this temperature being taken as image
temperature of the flame temperature;
The secondary air bathing the walls is preferably regulated by
action on the base plate apertures in such a manner that the two
previously mentioned regulations remain within a good operating
range;
In the case of recuperation of the sensible heat of the smoke, the
thermal load of the arrangement is regulated by action on the
damper of the exhaust fan.
Finally, the particular advantages obtained by operating in
accordance with the invention should be noted: Complete or partial
recuperation of the latent or sensible calories of low-value
gaseous by-products is effected, while creating a utilisable
negative pressure in their circuit;
These gaseous by-products, which are naturally dirty and polluting,
can be burned by recuperating the heat in large capacity units
giving rise to remarkably little or even to no pollution.
In an alternative of the smoke circuit it is possible to produce
the entire draught through the heat exchanger 4 by means of the
exhaust fan 43. In this case, the chimney is a forced draught
chimney, all the smoke from the combustion chamber 1 being drawn
into the heat exchanger 4. In this alternative the flame
temperature will be advantageously adjusted at 1200.degree. C.
* * * * *